s called
vitality, is very low, like a fire that has burned down, and if we go
out in the damp air and breathe the mists that rise from the ground our
vitality has not strength to resist them. But if we put fresh fuel on
our inward fire by eating something before we go out, then that bad
little mischief-maker, which we call malaria, has harder work to creep
into us."

"How funny! May I call Rap to tell him? Rap! Rap! come in and have milk
and something to eat, to make your inside fire burn up chills and
fever!"

Rap thought at first that Nat must be crazy, but very soon understood
what the Doctor meant, and was overjoyed at the prospect of having him
join the expedition.

"Dodo will cry when she wakes up and knows where we have gone," said
Nat, who had been much more kind and thoughtful of his sister since
coming to the Farm. But kindness is very catching, and at the Farm
everybody was kind, from the House People to the big gray horses in the
barn, which let the chickens pick up oats from between their powerful
hoofs, without ever frightening them by moving.

"It is too long a walk for little sister, but you must remember
everything that you see and hear, and tell her about it. Don't forget
the field-glass," said the Doctor, following the boys along the road
where telegraph wires made bird-perches between the high poles.

"You said a lot of birds came last night," said Nat to Rap; "but how do
you know that they came last night and where did they come from?"

"I know they came last night because they were not here yesterday,"
answered Rap; "but I don't know where they came from, except that it
must be from where it is warmer than it is here, because they went away
just before it grew cold last fall. See, Doctor, there are some of them
now on those fence rails and more up on the telegraph wires. The miller
calls them 'Bee Martins,' and says that they eat up all the honey-bees.
Have they any other name--because I have never seen them catch bees?"

Nat looked at them first with the field-glass, then without it as they
drew quite near the fence, and saw a fine bird, twice as long as his
middle finger. Its back and wings looked dark gray; it was white
underneath, with a touch of gray on the breast, and had a black tail,
with white at the end of it. As Nat looked the bird raised a little tuft
of feathers on top of its head, as if angry, flew into the air, giving a
shrill cry, seized an insect, and returned to its perch